Conventionally, inexpensive skin cleansing agents of fatty acid soaps having high cleansing performance and good foamability have been used as skin cleansing agents such as a facial wash. As raw materials of these skin cleansing agents, fatty acids (whose main components are saturated or unsaturated fatty acids having 8 to 18 carbon atoms) obtained by hydrolyzing natural fats and oils derived from plants and animals, such as beef tallow, coconut oil, palm oil and palm kernel oil, are mainly used.
Among fatty acid soaps prevalently used in skin cleansing agents containing fatty acid soaps as a main cleansing base, those of lauric acid (12 carbon atoms) or myristic acid (14 carbon atoms), which has a relatively short chain length, have defects such as giving a tight skin feeling after cleansing although they have a high water-solubility due to a low Krafft point. On the other hand, those of palmitic acid (16 carbon atoms) or stearic acid (18 carbon atoms), which has a longer chain length, have defects such as a low water-solubility and somewhat low foamability due to a high Krafft point although they give a mild feeling to skin.
No satisfactory cleansing compositions have been found so far in spite of the effort to develop cleansing compositions with improved foamability, safety, application feeling and the like, considering characteristics of these fatty acids. And thus a further improved cleansing composition has been desired.
Fatty acids having not less than 20 carbon atoms have seldom been used as a cleansing base due to their low water-solubility, insufficient foamability and unsatisfactory foam quality. However, there have been some proposals as described below. There have been some studies, for example, on transparent solid soaps incorporated with 0.5 to 6.0% by weight of a linear saturated fatty acid having 20 to 26 carbon atoms based on the total amount of fatty acids to enhance transparency of the solid soap (JP-A-59-75999); a pearl-like gloss dispersion having good storage stability, which contains 5 to 30% by weight of behenic acid and/or behenate salts (JP-A-10-226798, U.S. Pat. No. 5,998,354); a skin cleansing composition incorporated with 0.05 to 5% by weight of a saturated fatty acid having not less than 20 carbon atoms based on the total amount of the composition, to stabilize tone of the skin cleansing composition containing clay minerals (JP-A-1-149715); a skin cleansing agent incorporated with a specific higher fatty acid soap and a condensed ricinoleic acid polyglycerin ester, to improve stability thereof at high and low temperatures (JP-A-2002-68961); a hair conditioning shampoo composition containing 0.5 to 20% by weight of a fatty acid having a long chain of 18 to 36 carbon atoms (JP-A-5-255049, U.S. Pat. No. 5,360,581); and a solid cast composition containing 3 to 15% by weight of behenic acid soap (WO92/19712).